Resilient mounts of this type are known in the art, especially in the form of compression-type rubber metal mounts, and are employed, for instance, as engine mounts in motor vehicles. The reason for using engine mounts of this type is to improve the acoustic and vibratory comfort. If the choice is in favor of relatively hard rubber metal mounts, the advantage gained is that the low frequency vibrations are transmitted by the rubber metal mounts in a relatively rigid manner so that one need not be concerned about residual vibrations. Thus, the engine will not be subjected to residual vibrations and will not transmit objectionable low frequency vibrations to the body structure. However, the disadvantage of hard rubber metal mounts is that the high engine frequencies will also be transmitted, relatively unimpeded, onto the vehicle body, which adversely effects the acoustic comfort. If, on the other hand, one selects a relatively soft rubber metal mount, the high frequencies will be transmitted only to a very limited degree, and this means, in the case of motor vehicle engine mounts, that the higher natural acoustic vibrations generated by the engine are of little effect inside the vehicle, so that the acoustic comfort is correspondingly high. However, the engine will then be subjected to low frequency vibrations which may be induced, for instance, by the irregularities in the road surface. Thus, the low frequency comfort level in vehicles employing soft engine mounts is relatively poor.
Consequently, a rubber metal mount, i.e., a resilient mount alone is only a compromise between the conflicting demands of providing a soft as well as a rigid engine suspension.
Because of the aforementioned considerations, it has been proposed in the German publication No. DE-OS 29 27 757 to provide a space in the spring element for a magnetizable metal powder which is subjected to the magnetic field of a magnet attached to one of the mount retaining means provided for the engine mount. When this magnetic powder is magnetized by the electromagnet, it is compacted and impedes the resiliency of the spring element. This will then accomplish a variation of the spring characteristic of the engine mount. However, this arrangement is afflicted with the shortcoming that the metal powder, as it is subjected to the magnetic field, is merely hardened so as to form a solid body, without retaining any degree of elasticity. As a result, the spring element is subjected to a relatively high load because of the collision that occurs between it and the metal powder that has been solidified by the magnetic field, and it is therefore relatively difficult to control the spring characterisitcs of this prior art resilient mount.